The present invention relates to a refrigerating machine for developing extremely low temperature through the expansion of compressed fluid and, more particularly, to a fluid-operated refrigerator in which the pressure of the refrigerant is used for driving a displacer.
This refrigerating machine is adapted to perform a refrigeration cycle, so-called Gifford-McMahon cycle disclosed in the specifications of U.S. Pat. Nos. 2,966,035 and 3,188,819. This refrigeration cycle offers various advantages because it is actually carried out as a no-work cycle in which the work achieved by the expansion of the refrigerant is taken out in the form of heat but not in the form of mechanical work.
On the other hand, however, this Gifford-McMahon cycle imposes the following problem when the same is performed by a fluid-operated refrigerating machine. Namely, in such a case, it is extremely difficult to control the reciprocating motion of the displacer which operates as a free piston, so that the displacer often collides with the upper or lower end of the cylinder to generate vibration and noise.